In the prior art, a unit composed of a combination of an internal combustion engine with an electric motor, a unit using an electric motor as a prime mover and so on are known as a power unit of a vehicle. In order to control a drive torque and speeds of the internal combustion engine and the electric motor, a transmission is employed in a vehicle having the power unit of those kinds. One example is disclosed in Japanese Patent Laid-Open No. 2003-127681. The system disclosed in Japanese Patent Laid-Open No. 2003-127681 is a hybrid vehicle drive system in which an internal combustion engine is connected with a carrier of a planetary gear mechanism, and a first motor/generator is connected with a sun gear of the planetary gear mechanism. Also, a ring gear is connected with a member of an input side of a geared automatic transmission. A member of an output side of the automatic transmission is connected with a propeller shaft, and a second motor/generator is connected with the propeller shaft through a gear pair. Thus, according to the system taught by Japanese Patent Laid-Open No. 2003-127681, the planetary gear mechanism functions as a distribution mechanism distributing an engine power to the first motor/generator and to the output side. A torque is added or absorbed by a second motor/generator in the process of transmitting the power from the distribution mechanism to the automatic transmission. Japanese Patent Laid-Open No. 2003-127681 also discloses a configuration in which the automatic transmission is arranged between the second motor/generator and the propeller shaft, and the second motor/generator is connected to an input side of the automatic transmission.
Japanese Patent Laid-Open No. 2001-268853 discloses a structure in which a motor stator is arranged in a housing, an input shaft of a transmission is arranged coaxially with the motor stator, and the input shaft is inserted into a motor rotor facing to the motor stator.
In the electric motor and motor generator disclosed in the above-explained Japanese Patent Laid-Opens Nos. 2003-127681 and 2001-268853, a rotor having a permanent magnet is used. In case of inserting the above-explained rotor into an inner circumference of a stator, a magnetic force acts between the rotor and the stator. Therefore, it is difficult to keep those rotor and stator coaxially. According to the configurations taught by Japanese Patent Laid-Opens Nos. 2003-127681 and 2001-268853, the electric motor or the motor generator is connected directly with the gear pair, and the shaft of the automatic transmission or the drive shaft. Therefore, the rotor can be inserted into the stator while being centered by fitting the rotor onto the shaft or drive shaft. However, when the electric motor or the motor generator is thus assembled, the electric motor or the motor generator is connected with another mechanism such as the gear pair or the automatic transmission. For this reason, according to the conventional art thus far explained, an inspection and a tuning of the electric motor or the motor generator cannot be carried out in the process of assembling. Even if the inspection or the tuning can be taken place, an implementation thereof is rather difficult, and accuracy thereof may be deteriorated.